Furo[3,4-b]chromones, and not Pyrano[3,4-b]chromones, are Obtained by the Reaction of 3-Formylchromones with Isocyanides

Abstract

The reaction of formylchromones with alkyl isocyanides was reinvestigated. In earlier reports from other research groups, two different structures were proposed for the products of this reaction. Herein, we provide unambiguous evidence that these products are chromenylmethylene furochromenones and not pyrano­chromones. Our structure assignment is based on X-ray diffraction analysis and two-dimensional NMR methods. The knowledge of the correct structure of these compounds is essential for the design of derivatives with potential applications as bioactive molecules or fluorescent biomarkers.

Key words

cycloaddition reactions - furans - fused-ring systems - multicomponent reactions - heterocycles - natural products

• References and Notes

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• 16 General procedure for the cycloaddition of formyl-chromones and isocyanides: Isocyanide 2 (2.5 mmol) was added to a solution of formyl chromone 1 (5 mmol) in anhydrous THF (5 mL). The resulting solution was heated at reflux under N₂ for 5–8 h, and cooled to 0 °C. The precipitate was collected by filtration. An additional amount of product was recovered by concentration of the filtrate and purification by column chromatography
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